(a) Field of the Invention
The present invention relates to an accumulator in a vehicle automatic transmission and, more particularly, to an accumulator piston position detecting device of a piston type accumulator which permits a transmission control unit (TCU) to detect the displacement of the piston in real-time so as to use the detected data as information for determining a duty rate for applying hydraulic fluid to a friction element.
(b) Description of the Related Art
Generally, an automatic transmission includes a planetary gear system having several planetary gear sets and friction elements, such as clutches and brakes, for providing various forward and reverse speed ranges. To operate the friction elements, hydraulic pressure is used and a TCU controls the hydraulic pressure for applying or releasing the hydraulic pressure to or from the clutches and brakes.
FIG. 4 shows a friction element of an automatic transmission. As shown in FIG. 4, the friction element 50 includes an accumulator 60 having a plug 61 and spring 62 such that the accumulator regulates hydraulic pressure applied to the friction element 50.
The hydraulic pressure applied to the friction element 50 is controlled by a duty control signal from the TCU, which produces the duty control signal on the basis of data detected by various sensors for sensing vehicle conditions and derived piston displacement data.
That is, the TCU determines whether or not the friction element 50 is engaged on the basis of the derived piston displacement data.
In this case, the TCU uses a derived value calculated on the basis of an oil temperature calibration factor and an engine revolution per minute (rpm) calibration factor with derived piston displacement data saved in memory for determining engagement of the friction element.
However, since the stroke displacement is not detected in real-time, the determination by the TCU as to whether or not the friction element is engaged is not precise. Accordingly, the duty ratio for controlling hydraulic pressure cannot be precisely calculated.
The present invention has been made in an effort to solve the above problem of the prior art.
It is an object of the present invention to provide an accumulator piston displacement detecting device and method thereof by which the TCU can precisely control the hydraulic pressure so as to minimize shift shock and improve shift performance, resulting in ride comfort of a vehicle.
To achieve the above object, the accumulator piston displacement detecting device for an automatic transmission of the present invention comprises a friction element, a hydraulic line for supplying and releasing hydraulic pressure to the friction element, an accumulator connected to the friction element through the hydraulic line for regulating the hydraulic pressure being supplied to the friction element, a switch installed in a portion of the accumulator, and a TCU for controlling the hydraulic pressure supplied to the friction element on the basis of a signal from the switch.